1. Field of the Invention
The present invention relates to a communication apparatus that executes a directivity angle search for determining antenna directivity characteristics suitable for communication, a communication system, a control method, and a storage medium.
2. Description of the Related Art
In recent years, there has been increasing demand for high-speed and real-time data communication for, for example, transmission of uncompressed high-definition moving image data or the like. To deal with this demand, a communication system using high frequency bands including millimeter wavebands is gathering attention. Because the millimeter wavebands have shorter wavelengths than the frequency bands for 2.4- and 5-GHz wireless LAN compliant with IEEE 802.11, attenuation of radio waves due to radio-wave propagation readily increases. Thus, in order to secure a sufficiently long communicable distance, a communication system using antennas such as array antennas that have variable directivity characteristics has been proposed (IEEE 802.15.3c-2009). In order to enable transmitter-receiver communication using antennas having variable directivity characteristics, it is necessary for the transmitter and the receiver to determine the directions of arrival of direct waves and reflected waves.
IEEE 802.15.3c-2009 describes a technique for specifying the direction of arrival of radio waves by beforehand providing a period for determining directivity characteristics to be used in communication between a transmitter and a receiver and scanning the antenna directivity characteristics of the receiver for each antenna directivity characteristic of the transmitter. Hereinafter, this technique is referred to as a “directivity angle search”. By performing a directivity angle search, transmission/reception directivity characteristics that enable radio wave reception at the desired reception quality can be determined, and a plurality of those directivity characteristics can be stored as communication path information and used in subsequent data communication.
Japanese Patent Laid-Open No. 2003-283404 discloses a technique for creating a delay profile for each antenna directivity characteristic and determining, based on the delay profiles, an element antenna weight value that forms a directivity characteristic having a narrower beam width for the next-to-be-executed directivity angle search. In the technique of Japanese Patent Laid-Open No. 2003-283404, this processing is repeated to enable high-precision detection of communication paths. Japanese Patent Laid-Open No. 2001-345747 discloses a technique for creating a delay profile for each antenna directivity characteristic so as to detect an effective communication path and, with use of a demodulation time that corresponds to the obtained communication path and the antenna directivity characteristic, demodulating a signal with a demodulator that is assigned to each communication path. The technique of Japanese Patent Laid-Open No. 2001-345747 uses a different communication path depending on the antenna directivity characteristic, thereby reducing interference on signals transmitted from a mobile station to a base station caused by signals from other mobile stations. In this way, with conventional techniques, the direction-of-arrival estimation of radio waves and determination of antenna directivity characteristics to be used has been performed using delay profiles of received signals.
A communication system that requires frequent directivity angle searches could be required to achieve low power consumption when performing directivity angle searches. However, with the conventional techniques, when a directivity angle search is performed, the receiver operates irrespective of whether or not radio waves have arrived. Thus, there is a problem that more power than necessary may be consumed.
The present invention has been conceived in view of the above-described problem and provides a technique for reducing power consumption associated with directivity angle searches, using delay profiles of received signals.